This invention relates to the structure of an exhaust muffler for use in an engine having two exhaust ports for connection to the muffler.
For an engine having two or more cylinders, the muffler is generally connected to the engine body via either one or two exhaust pipes. To enhance the noise muffling effect, the muffler and the engine body are usually positioned so as to be separated by a certain distance. Then, by positioning such peripheral components as the carburetor, fuel pump, and coolant pump, and such hose as the fuel line and the coolant lines, or such covers as the fan housing, in the space between the muffler and engine body, a layout is achieved whereby the entire engine is compact.
In an engine wherein the muffler is connected to the cylinders via two exhaust pipes, the two exhaust pipes have been routed as most appropriate for each engine while considering the layout of the aforementioned peripheral devices or of the support frame, etc. The two exhaust pipes have always been connected to the muffler within an area of about one-fourth to three-fourths the overall length of the muffler.
However, with this type of muffler structure, because an arrangement was used wherein the muffler is supported on the engine body by the exhaust pipes, from the viewpoint of strength, the support of the muffler, which has a considerable amount of weight, by the two exhaust pipes connected at the center of the muffler, placed excessive demands on the strength of the joints between the exhaust pipes and the muffler body under the state of vibration which exists during engine operation, thus resulting in a reduction in the life of the exhaust pipes. In addition, the rigidity of the muffler and the exhaust pipe structure was low, thus resulting in an increased amount of noise caused by the resonance of the muffler and the exhaust pipes during engine operation.
Furthermore, because of the short distance which existed between the two exhaust pipes, the heat emanating from the exhaust pipes caused an undesirable increase in the temperature of the above-mentioned peripheral components, hose and covers. This especially led to the early deterioration of the parts made of rubber and covers made of plastic, etc.
Note that, although there are examples of prior art mufflers wherein first expansion chambers are provided at both ends of the muffler and the exhaust pipes are connected to the two ends, such as that shown in FIG. 7 herein, in this case, there was the drawback that, in order to provide the needed capacity of the two first expansion chambers and to handle the exhaust pipes, the overall length of the entire muffler, including the exhaust pipes was increased.
The main objective of this invention is to provide a muffler apparatus which avoids the problems described above, and for which the overall length of the muffler is relatively short without any loss in the noise muffling effect.